Ground fault detection in ungrounded power systems

ABSTRACT

Methods, systems, and apparatus, including computer programs stored on a computer-readable storage medium, for obtaining, from an electric field sensor, measurements of a net electric field resulting from a combination of respective electric fields from two or more electrical power conductors that are proximate to the electric field sensor. The apparatus detects a change in successive measurements of the net electric field. The apparatus determines, based on the change, that an electrical fault has occurred in one of the two or more electric power conductors. The apparatus sends to a server system, data indicating that the electrical fault has occurred in one of the two or more electric power conductors.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/200,863, entitled “GROUND FAULT DETECTION IN UNGROUNDED POWERSYSTEMS”, filed Nov. 27, 2018, which is incorporated herein by referencein its entirety.

BACKGROUND

Electrical faults in electrical power systems can cause damage to systemcomponents, and, possibly, injury to personnel. Early detection offaults is critical to maintaining the safe operation of such systems.For example, electrical faults such as reduced impedance to ground cancreate significant increases in the electrical current passing throughan electrical power system. In some cases, the increase in the currentcan be of a sufficient magnitude to cause real and permanent damage tothe system and injury to personnel.

SUMMARY

In general, the disclosure relates to detecting electrical faults inelectric power transmission systems. More specifically, the disclosurerelates to a non-contact ground monitoring device (GMD) and operationsof a GMD. A GMD monitors power transmission lines for electrical faultsthat cause or could potentially cause an electrical ground. Anelectrical ground in a power transmission system creates the potentialfor serious damage to the system and injury to humans and animals if theground is not corrected promptly. A GMD can detect grounds in powertransmission lines without making physical contact with the transmissionlines.

In general, innovative aspects of the subject matter described in thisspecification can be embodied in a ground fault detection device thatincludes an electric field sensor, a power source, and a control system.The control system is coupled to the electric field sensor and the powersupply. The control system includes one or more processors and a datastore coupled to the one or more processors. The data store hasinstructions stored thereon which, when executed one or more processors,causes the one or more processors to perform operations that include:receiving an output signal from the electric field sensor, the outputsignal indicating a value of a net electric field resulting from acombination of respective electric fields from two or more electricalpower transmission lines that are proximate to the electric fieldsensor; detecting, based on a change in the output signal, an electricalfault in one of the two or more electrical power transmission lines; andsending, to a server system, data indicating detection of the electricalfault.

This and other implementations can each optionally include one or moreof the following features.

In some implementations, detecting the electrical fault includesdetermining that a magnitude of the output signal is greater than amagnitude of a previous output signal.

In some implementations, the change in the output signal is a deviationfrom an approximately zero net electric field measurement.

In some implementations, detecting the electrical fault includesdetermining that the output signal is greater than a threshold value.

In some implementations, the electric field sensor is one of: acapacitor based electric field sensor, an electro-optical electric fieldsensor, a Micro-Electro-Mechanical Systems electric field sensor, or anantenna electrode sensor.

In some implementations, the power source includes a battery or a solarcell.

In some implementations, the operations include determining a severityof the electrical fault by comparing the output signal with a pluralityof threshold values, each threshold value in the plurality beingassociated with a respective fault severity level.

In some implementations, the operations include identifying theelectrical fault as an intermittent fault. In some implementations, theoperations include sending fault characteristics to the server system inresponse to identifying the electrical fault as an intermittent fault.In some implementations, the fault characteristics include dataindicating one or more times at which the electrical fault is detectedand one or more times at which the electrical fault is no longerdetected. In some implementations, the fault characteristics includedata indicating a magnitude of the electrical fault at times when theelectrical fault is detected.

In some implementations, identifying the electrical fault as anintermittent fault includes comparing a series of output signalsmeasured over a period of time, and determining that individual outputsignals in the series of output signals indicate repeated increases anddecreases in the net electric field measured by the electric fieldsensor.

In some implementations, the operations include calibrating the deviceby: obtaining a series of output signals from the electric field sensorover a period of time, each output signal in the series of outputsignals indicating a value of a net electric field proximate to theelectric field sensor at a respective time during the period of time;determining, from the series of output signal, a baseline net electricfield value; and adjusting one or more fault detection thresholds basedon the baseline net electric field value.

In some implementations, the data indicating detection of the electricalfault includes location data indicating a geographic location of thedevice.

In another general aspect, innovative aspects of the subject matterdescribed in this specification can be embodied in methods that includeactions of obtaining, from an electric field sensor, measurements of anet electric field resulting from a combination of respective electricfields from two or more electrical power conductors that are proximateto the electric field sensor. Detecting a change in successivemeasurements of the net electric field. Determining, based on thechange, that an electrical fault has occurred in one of the two or moreelectric power conductors. Sending, to a server system, data indicatingthat the electrical fault has occurred in one of the two or moreelectric power conductors. Other implementations of this aspect includecorresponding systems, apparatus, and computer programs, configured toperform the actions of the methods, encoded on computer storage devices.

These and other implementations can each optionally include one or moreof the following features.

In some implementations, determining that the electrical fault hasoccurred in one of the two or more electric power conductors includesdetermining that a magnitude of at least one of the successivemeasurements is greater than a magnitude of a previous measurement.

In some implementations, the change in the successive measurements ofthe net electric field is a deviation from an approximately zero netelectric field measurement.

In some implementations, determining that the electrical fault hasoccurred in one of the two or more electric power conductors includesdetermining that at least one of the successive measurements is greaterthan a threshold value.

Some implementations include determining a severity of the electricalfault by comparing at least one of the successive measurements with aplurality of threshold values, each threshold value in the pluralitybeing associated with a respective fault severity level.

Among other advantages, implementations may improve the overall safetyof electrical power systems, e.g., power transmission and distributionssystems. For example, non-contact GMDs can provide early warnings ofdangerous conditions in electrical power systems. Implementationsprovide for less intrusive fault monitoring electrical power systems.For example, non-contact GDMs do not require physical electricalconnections to the electrical power systems that they are installed tomonitor. Moreover, non-contact GMD systems may provide the ability tomonitor for grounds at more locations along a power systems.Accordingly, implementations may provide for more robust and reliableelectrical fault monitoring systems.

The details of one or more embodiments of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages of thesubject matter will become apparent from the description, the drawings,and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary electrical fault detection system100 according to implementations of the present disclosure.

FIG. 2A is a block diagram of an example non-contact ground monitoringdevice (GMD) according to implementations of the present disclosure.

FIG. 2B is a schematic diagram of an example electric field sensoraccording to implementations of the present disclosure.

FIG. 3A is a diagram illustrating exemplary normal operating conditionsof a GMD according to implementations of the present disclosure.

FIG. 3B is a diagram illustrating exemplary fault detection operationsof a GMD according to implementations of the present disclosure.

FIG. 3C is a diagram illustrating exemplary fault detection operationsof a GMD 102 for detecting an exemplary fault and determining a severityof the fault according to implementations of the present disclosure.

FIG. 3D is a diagram illustrating exemplary fault detection operationsof a GMD for detecting an intermittent fault according toimplementations of the present disclosure.

FIG. 4 is a flow diagram that illustrates example processes fordetecting electrical faults in electrical power systems according toimplementations of the present disclosure.

FIG. 5 depicts a schematic diagram of a computer system that may beapplied to any of the computer-implemented methods and other techniquesdescribed herein.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

A fault in an electrical power system (e.g., a ground fault) creates thepotential for serious damage to the system and injury to humans andanimals if the ground is not corrected promptly. In ungroundedelectrical power systems, e.g., ungrounded AC or DC electrical powertransmission and distribution systems, one electrical ground will notresult in a short circuit. However, if a second electrical ground occursbefore the first is corrected a short circuit may occur and create theexcessive current which can damage equipment or injure personnel. Inother words, early detection of the first electrical ground inungrounded systems can aid in preventing potentially dangeroussituations before a subsequent ground occurs.

More specifically, ungrounded systems have the distinct advantage thatthe first fault to ground is essentially “free.” The electrical powersystem can keep operating while the first ground is located andcorrected. However, a second fault to ground, if of sufficiently lowimpedance, can cause a ground fault, which can create sufficiently highcurrents to trip system protection relays and bring the system downuntil the faults can be located and fixed. Furthermore, excessively highfault currents can cause permanent damage to the conductors, insulators,and/or protection devices in the electric power system. This secondfault also has the potential to cause damage to anything in the currentcarrying path which, in addition to electrical components, can includevegetation such as tree limbs or bushes that can lead to the initiationof fires.

Ground faults are caused by low impedances between current carryingconductors and the ground. For example, low impedances to ground can becaused by dirt/contamination across insulators, encroachment with powerlines that lead to contact with vegetation, and damaged conductors orinsulators leading to contact with grounded components.

FIG. 1 is a diagram of an exemplary electrical fault detection system100. The system 100 includes non-contact ground monitoring devices(GMDs) 102 a, 102 b (collectively 102) in communication with a serversystem 106, and one or more user computing devices 108. The GMDs 102 areground detection devices that can detect a ground in an electrical powersystem by monitoring electric fields generated by an electrical powersystem. For example, multiple GMDs (e.g., GMD 102 a and GMD 102 b) arepositioned proximate to power transmission lines 104 at variouslocations in an electrical transmission and distribution (T&D). To beproximate to the power transmission lines 104 a GMD 102 is not in directcontact with the transmission lines 104, but is sufficiently close tothe power transmission lines 104 so that electric fields generated bythe transmission lines are measurable by an electric field sensor of theGMD's 102. The actual distance between a GMD 102 and the powertransmission lines 104 that the GMD 104 is installed to monitor may varydepending on various factors including, but not limited to, theoperating voltage of the power transmission lines 104, the sensitivityof a GMD's 102 electric field sensor, and the amount of electricalinterference at the location.

The GMDs 102 can be placed so as to establish a network of GMDs 102 formonitoring various portions of the T&D system for electrical faults(e.g., electrical grounds). The GMDs 102 communicate information to theserver system 106. For example, each GMD 102 a, 102 b in a GMD networkcan communicate information related to the status of electrical faultsat their respective locations of the T&D system. The server system 106analyzes the information received from GMDs 102 in the network and canalert appropriate personnel (e.g., utility maintenance workers) upon oneor more of the GMDs 102 detecting a fault condition. For example, theserver system 106 can send an appropriate alert to computing devices 108associated with such personnel.

The server system 106 can include a system of one or more computers. Theserver system 106 is configured to identify and, in someimplementations, locate an electrical fault (e.g., a ground) based ondata obtained from a network of GMDs 102. In some implementations, GMDs102 send data indicating detections of electrical faults to the serversystem 106 to permit notifications being sent to proper personnel. Insome implementations, the server system 106 can use fault detectionsfrom a series of GMDs 106 in a network to estimate the location of anelectrical fault. For example, the server system 106 can store andexecute software to analyze data from a network of GMDs to identify asection of a T&D system in which the fault likely located. In someimplementations, the server system 106 can use timing informationreceived from each of a set of GMDs 102 that indicate a fault conditionto identify a section of a T&D system in which the fault likely located.For example, when a GMD 102 detects a fault condition, the GMD 102 cansend timing data indicating the time of the fault detection. The serversystem 106 can compare timing information received from several GMDs 102indicating faults within a similar geographical area to aid withlocalizing the fault. Furthermore, the server system 106 can providealerts of detected electrical faults with an estimated location of thefault to appropriate personnel. For example, the server system 106 canstore and execute one or more machine learning engines that areprogramed to estimate a likely location of a detected electrical faultwithin a T&D system.

User computing devices 108 can be computing devices including, e.g.,mobile phones, smart phones, tablet computers, laptop computers, desktopcomputers, or other portable or stationary computing device. The usercomputing devices 108 can feature a microphone, keyboard, touchscreen,speaker, or other interfaces that enable users to provide inputs to andreceive output from user device 108. For example, the user computingdevices 108 can be associated with a utility company or specific utilitycompany personnel. The user computing devices 108 can be configured toreceive information from the server system 106 related to faultindication detected by one or more GMDs 102. For example, the usercomputing devices 108 can include a software application configure toprovide associated users with information related to electrical faultsdetected by a network of GMDs 102.

GMDs 102 can detect grounds in power transmission lines without makingphysical contact with the power lines 104. A GMD 102 operates bydetecting the net electric field generated by a set of power lines 104(e.g., two lines in a two-phase, or split-phase, system or three linesin a three-phase system). When operating properly (e.g., without anelectrical fault), the net electric field of the power lines 104 will beapproximately zero. For example, the net electric field may deviate fromzero slightly due to normal variations in amplitude and phase of theelectrical power being transmitted in the power lines 104 yet stillconsidered to be approximately zero. For instance, variations can occuras electrical power demand changes in the power system. However, if anelectrical fault occurs on one of the lines, the electric fields of theindividual lines becomes unbalanced causing the net electric field tochange, and in some instances to change dramatically and suddenly. TheGMD 102 detects the changes in the net electric field and can detect theexistence of an electrical fault from the power lines 104 to groundbased on such changes.

GMDs 102 can be positioned at various locations to monitor differentsections of a T&D system. For example, a GMD 102 a can be installeddirectly on the ground or on a stand between two power line supportstructures 112. As illustrated in FIG. 1, in some implementations, a GMD102 a is coupled to an electrical ground 110 to, e.g., provide areference for fault detection. In other implementations, a GMD 102 maynot be connected to an electrical ground, but may be electricallyfloating. In some examples, a GMD 102 b can be mounted on a supportstructure 112. For example, GMD 102 b is illustrated as being mounted toa power line 104 support structure 112. A support structure mounted GMD102 b can be coupled to a grounding cable attached to the supportstructure 112, if desired. For example, ungrounded T&D systems oftenhave a grounding cable for attached to the support structures 112 forpurposes other than grounding the power lines 104 themselves. Asdiscussed in more detail below, the GMDs 102 b, such as those installedon a support structure 112 may need to establish a baseline electricfield measurement from the associated power lines 104 due tointerference caused by conductive objects nearby (e.g., a metal supportstructure). In other words, nearby metal objects may interfere with theindividual electric fields generated by each the power lines 104 duringnormal (un-faulted) operating conditions such that the net electricfield deviates from zero. To accommodate, the GMD 102 b can becalibrated to establish a baseline “normal” net electric field from thepower lines 104 for the area where the GMD 102 b is installed.

FIG. 2A is a block diagram of an example non-contact GMD 102. The GMD102 includes an electric field sensor 202, a controller 204, memory 206,a power source 208, a communication interface 210, and, optionally, alocation sensor 212. The power source 208 can be, but is not limited to,a battery (or battery bank), a solar power source, or an A/C powersource configured to receive power from the power lines 104. Thecommunication interface 210 is a network interface. For example, thecommunication interface can be a cellular network interface, a localarea network interface (e.g., Wi-Fi interface), a fiber optic interface,or another appropriate networking interface. The location sensor 212 isconfigured to determine the geographical location of the GMD 102. Forexample, the location sensor 212 can be a Global Positioning System(GPS) sensor. In some examples, the location sensor 212 is not required.For example, the location of the GMD 102 can be determined usingnetworking based location detection, such as cellular triangulation ofWi-Fi positioning systems.

The electric field sensor 202 is configured to measure the magnitude ofan electric field present in the vicinity of the GMD 102. The electricfield sensor 202 can be, e.g., a parallel plate capacitor based sensor,an electro-optical electric field sensor, or a MEMS(Micro-Electro-Mechanical Systems) electric field sensor, or an antennastyle sensor.

The controller 204 is configured to control the operations of the GMD102 as described herein. For example, the controller 204 can include oneor more processors or microcontrollers configured to execute softwareinstructions stored in the memory 206. The controller 204 is coupled tothe electric field sensor. The controller 204 receives output signalsfrom the electric field sensor 202 and processes the signals todetermine whether the received signals indicate the existence of anelectrical fault, as described in more detail below. In someimplementations, the controller 204 controls the operations of theelectric field sensor 202. For example, the controller 204 can controloperations of the electric field sensor 202 including, but not limitedto, the sampling frequency, the sample period, and calibration of thesensor. The controller 204 can also control the operations of thecommunication interface 210 and the location sensor 212.

FIG. 2B is a schematic diagram of an example electric field sensor 202.FIG. 2B illustrates an example parallel capacitor based electric fieldsensor 202. The electric field sensor 202 includes a capacitor 252electrically connected to an electronics switch, e.g., a transistor 256,and sensor control circuitry 258 configured to control the operation ofthe sensor 202. One of the capacitor 252 electrodes is, optionally,coupled to ground and the other electrode 256 is connected to an inputterminal T1 of the transistor 254. The output terminal T2 of thetransistor 254 is connected to a measurement input of the sensor controlcircuitry 258. The control terminal G1 of the transistor is coupled to acontrol signal output of the sensor control circuitry 258.

The electric field sensor 202 operates by collecting charge on thecapacitor 252 from an electric field near the sensor 202. The electricfield sensor 202 samples the stored change by turning the transistor 254on and allowing the capacitor to discharge. The magnitude of theexisting electric field is related to the amount of change stored on ordischarged by the capacitor 254. Specifically, the magnitude of themeasured electric field is proportional to the change density on thecapacitor. The sensor control circuitry 258 samples the capacitor 252,e.g., by turning the transistor 254 on, at a frequency sufficient tomeasure changes in the net electric field. For example, the sensorcontrol circuitry 258 can sample the capacitor 252 at a frequencysufficiently high to avoid aliasing problems with the frequency of theAC power signal being used by a monitored electric power system. Thesensor control circuitry 258 measures the amount of change dischargedwhen the capacitor is sampled. In some implementations, the GMD 102enters a low power or “sleep” mode between samples. Suchimplementations, will extend the battery life of battery powered GMDs102.

The sensor control circuitry 258 sends measurement data representing themeasured capacitor charge to the controller 204. The measurement datacan be, e.g., analog or digital voltage values representing themagnitude of the measured charge. In some implementations, thecontroller 204 queries the sensor 202 for measurements at time intervalsthat are different form the sensor's sampling period. For example, thecontroller 204 can be configured to request measurement data atdifferent intervals depending on different criteria including, but notlimited to, whether the GMD 102 has detected an electrical fault, timeof day, the state of charge of the GMD's power source 208, or acombination thereof. For example, the controller 204 can be configuredto increase the frequency measurement data requests upon the detectionof an electrical fault. In some implementations, the electric fieldsensor 202 (e.g., sensor control circuitry 258) or the controller 204can evaluate the magnitude of the measured electric field.

FIG. 3A is a diagram illustrating exemplary normal operating conditionsof a GMD 102. FIG. 3A illustrates the GMD 102 positioned below threeconductors 302 of an exemplary 3-phase AC power line 104 system. Eachconductor 302 carries one phase of AC current; phase A, phase B, orphase C. Furthermore, the current in each phase is driven by acorresponding alternating voltage with respect to ground. In athree-phase system, for example, the voltage waveform in each phase is120 degrees out of phase with the others. For example, phase A may havea zero degree phase angle, phase B may have a 120 degree phase angle,and phase C may have a 240 degree phase angle. Each conductor 302 alsogenerates a respective electric field 304 that varies in synchronizationvoltage with respect to the ground in the phase. So, the electric fieldgenerated by the phase B conductor 302 will be 120 degrees out of phasewith that generated by the phase A conductor 302.

Graph 310 illustrates the amplitude variations of the respectiveelectric fields generated by the phase A, phase B, and phase Cconductors 302. As shown, the voltage potential in the conductors 302,and by extension, the electric fields generated by the voltage arebalanced by having equivalent magnitudes and being 120 degrees out ofphase with each other, consequently the net electric field measured bythe electric field sensor 202 is zero or near zero (“Measured E-field”).That is, the three separate electric fields 304 generated by thechanging voltage in the conductors 302 nominally sum to zero duringnormal operations. Consequently, when the electric field sensor 202 ofthe GMD 102 measures zero or near zero electric field there is noindication of an electrical fault.

For example, the electric fields 304 of each of the three phases (phasesA, B, and C) will tend to cancel each other out, producing a near-zeronet electric field at the electric field sensor 202. Therefore, undernormal operations, and assuming no external electrical interference withthe field from the support structure, the electric field sensor willgenerally measure a near-zero electric field when sampled. For acapacitor based electric field sensor 202, the capacitor 252 will buildup only a minimal amount of change (if any) due to the near-zero netelectric field of the electrical power system near the sensor 202. Whenthe GMD 102 samples the electric field sensor 202 only a minimal amountof change will be discharged from the capacitor 252 indicating that alow magnitude net electric field has been measured.

In response to detecting a normal, ungrounded state, the GMD 102 may nottransmit any updates to the server system 106. However, in someimplementations, the GMD 102 can occasionally transmit data to theserver system 106 indicating that no fault conditions have beendetected. For example, the GMD 102 may occasionally transmit a negativereport (e.g., that no faults have been detected) as a “liveness” signalto indicate to the server system 106 that the GMD 102 is operatingproperly and that the lack of transmission is not due to a failure ofthe GMD 102 itself.

FIG. 3B is a diagram illustrating exemplary fault detection operationsof a GMD 102. When one phase of an ungrounded three-phase AC powersystem becomes grounded by, e.g., experiencing a low impedance toground, the phases of the power system become unbalanced. For example,graph 320 illustrates phase A as being completely grounded, by having avery low impedance to ground. Thus, the voltage with respect to groundin phase A drops to zero (or near zero). In addition, the correspondingvoltage to ground in phases B and C will likely increase. However, whenthe AC power system becomes unbalanced, the individual electric fieldsgenerate by each phase no longer sum to zero at the GMD's 102 electricfield sensor 202. Instead, the Measured E-field will deviate from zeroin proportion to the significance of the electrical ground. In theexample illustrated, the voltage of the phase A conductor 302 hasdropped to zero indicating that a short circuit to ground has occurredat some location along the phase a conductor 302. For example, theinsulation of the phase A conductor 302 may be damaged and a directelectrical path to ground may have occurred.

In the presence of a significant electrical fault, as illustrated, theelectric fields 304 of each of the two unaffected phases (e.g., phasesB, and C) will tend to reinforce each other, producing a non-zero netelectric field at the electric field sensor 202. The GMD 102 can detectthe electrical fault in the power system, by detecting the change in thenet electric field. For example, the GMD 102 can detect that themagnitude due to the net electric field measured by the electric fieldsensor 202 has increased from the previous measurement. In response, theGMD 102 can transmit data to the server system 106 indicating that anelectrical fault has likely occurred along a portion of the electricalpower system that the GMD 102 is installed to monitor. In someimplementations, the GMD 102 can send location data to the server system106 along with the indication of the detected fault. Locationinformation can include, but is not limited to, GPS data, Wi-Fipositioning data, a serial number of the GMD 102, or a combinationthereof. As discussed below, the server system 106 can use the locationdata of the GMD 102 to aid in identifying possible locations of theelectrical fault along the conductors 302.

For example, a capacitor based electric field sensor 202 will measurethe increased net electric field by building up a significant amount ofcharge due to the increased magnitude of the net electric field if thepower system becomes unbalanced. When the GMD 102 samples the electricfield sensor 202 an amount of charge that is proportional to theincreased magnitude of the net electric field near the sensor 202 willbe discharged from the capacitor 252, thus, indicating the increase inthe magnitude of the net electric field.

The GMD 102 can detect the increase in the magnitude of the net electricfield given off by the power system by, for example, comparing thesubsequent electric field measurements to previous electric fieldmeasurements and detecting the increase in the net electric field. Insome implementations, the GMD 102 can detect the increase in themagnitude of the net electric field given off by the power system bycomparing electric field measurements to one or more threshold values.For example, the GMD 102 can store a table of threshold net electricfield measurement values each indicative of a different severity levelof an electrical fault. In some implementations, the GMD 102 comparessubsequent electric field measurements to prior measurements as a firstorder check to identify a change in the magnitude of the measured netelectric field, and, upon detecting an increase, compares the measuredelectric field value to one or more threshold values to determine apotential severity of a corresponding electrical fault.

FIG. 3C is a diagram illustrating exemplary fault detection operationsof a GMD 102 for detecting an exemplary fault and determining a severityof the fault. Graph 330 illustrates a potentially minor electricalfault. For example, the electric field generated by phase A of theelectric power system is slightly reduced, for example, due to aslightly reduced impedance to ground along the phase A conductor 302.However, even the slight reduction in the magnitude of the electricfield generated from the phase A conductor 302 causes a minor imbalancein the net electric field measured by the electric field sensor 202. Asillustrated, the magnitude of the Measured E-Field increases slightly.As noted above, the GMD 102 can detect this increase in the MeasuredE-Field, by, for example, comparing the present Measured E-Field valuewith a previous electric field measurement to detect the increase. In asimilar manner, the GMD 102 can detect that an electrical fault has beencorrected by comparing the present Measured E-Field value with aprevious electric field measurement to detect a decrease in themagnitude net electric field.

Graph 330 also illustrates example fault detection threshold values 332,334 for determining the potential severity of an electrical fault. Asindicated above, the magnitude of the net electric field measured by theGMD 102 can serve as an indication of the severity of a potentialelectrical fault. For example, an electrical ground is generally moresevere with a lower electrical impedance between a conductor 302 andground. This relative reduction in impedance to ground created by anelectrical fault may manifest itself in the amount of decrease in thevoltage to ground of the affected phase. The GMD 102 can measure theseverity based on the amount by which the net electric field increasesdue to the reduction in the voltage to ground of the affected phase.

For example, a measured net electric field that meets or exceeds thefirst threshold value 332 may indicate a minor electrical fault. A minorelectrical fault may be one that should be corrected, but does notrequire urgent attention because the impedance to ground is stillsufficient to prevent excessive current surges if a second ground wereto occur. By contrast, a measured net electric field that meets orexceeds the second threshold value 334 may indicate a major electricalfault. A major electrical fault may be one which should be correctedimmediately to prevent potentially damaging current surges if a secondground were to occur before the detected fault is corrected.

In some implementations, the GMD 102 can send fault characteristic datato the server system 106 when reporting fault indications. For example,fault characteristic data can include, but is not limited to, dataindicating the severity of potential faults. In some implementations,the GMD 102 can send the actual electric field measurement data to theserver system 106. The server system 106 can use the electric fieldmeasurement data to determine the severity of the potential faults by,e.g., using a similar process of comparing to fault detection thresholdvalues.

In some implementations, the threshold fault detection values mayprovide a mechanism for avoiding excessive false positive faultdetections. For example, the measured electric field may deviate from anear-zero value due to an external electrical interference such as anobject passing between the conductors 302 and the GMD 102. However,deviations due to external interference may not be sufficient to causemeasured net electric field to exceed the first threshold value 332.Accordingly, the use of threshold values to aid in detecting significantchanges in the net electric field can provide an allowance for somelevel of deviation in the net electric field measurements withoutcausing the GMD 102 to generate unnecessary fault detectionnotifications.

In some implementations, the GMD 102 can calibrate the fault detectionthreshold values. For example, the GMD 102 can calibrate the faultdetection threshold values to account for effects of external factors onthe net electric field near a location at which the GMD 102 isinstalled. For example, GMDs 102 installed on support structures 112 mayexperience interference from metal contained in the support structures112 or from other nearby metal objects. For example, nearby metalobjects may interfere with the electric fields generated by each phaseof the electric power system and cause the net electric field to appearunbalanced. As another example, electric fields the GMD 102 may bepositioned at a location below the power line conductors 302 (or to theside if the power lines are configured vertically) where the electricfields are slightly asymmetric such as being off set to one side orpositioned at a too close the field of the closest wire will bedominant. In such situations, the “normal” net electric field measuredby a GMD 102 under non-fault conditions may be greater than thatmeasured by a GMD 102 in locations that do not contain such interferingobjects or by a GMD 102 positioned in a location where the electricfields are substantially symmetric. In some implementations, a GMD 102can calibrate fault detection threshold values for its particularlocation by adjusting the fault detection threshold values based onmeasurements of the net electric field under known non-fault conditionsover a period of time. For example, a GMD 102 can average a series ofmeasurements performed over a calibration period to establish a baselinenet electric field measurement for non-fault conditions. The faultdetection threshold values for that particular GMD 102 can then beincreased based on an established baseline net electric field value. Forexample, the fault detection threshold values can be increased by theestablished baseline net electric field value, or by an appropriatefactor of the baseline value.

FIG. 3D is a diagram illustrating exemplary fault detection operationsof a GMD 102 for detecting an intermittent fault. Graph 340 illustratesan example of electric field measurements from an electric field sensor202 if the power supply system experiences an intermittent fault. Forexample, an intermittent ground fault can be caused by intermittentcontact between one of the conductors 302 (e.g., the phase A conductor302) with a low impedance path to ground. For instance, during highwinds one of the conductors 302 may intermittently come in contact withan object (e.g., a damp tree branch) creating a conductive path toground. Such intermittent contact can cause the magnitude of the voltagein the affected conductor 302 to decrease, and, by extension, cause themagnitude of the electric field generated by the conductor to decrease.Consequently, the electric field sensor 202 will measure intermittentincreases in the magnitude of the net electric field (e.g., as shownduring times 342 and 344). Such measurements may appear to the GMD 102as if a fault is being repetitively detected and cleared.

In some implementations, a GMD 102 can detect an intermittent fault bycomparing a series of net electric field measurements over a period oftime to identify indications of repeated increases and decreases in thenet electric field measurements. In some implementations, the GMD 102records characteristics of the intermittent fault including, but notlimited to, the magnitude of the net electric field when the fault isdetected, changes in the magnitude of the net electric field, times atwhich the fault detections occur, times at which the fault clears, or acombination thereof. In some implementations, the GMD 102 sends thecharacteristics of the intermittent fault to the server system 106. Insome implementations, the GMD 102 or the server system 106 can use thecharacteristics of the intermittent fault to identify potential causesof the fault. For example, the GMD 102 or the server system 106 cancorrelate the characteristics of the intermittent fault with known faultcharacteristic to identify a potential cause of the fault.

In some implementations, the server system 106 can obtain weather datafor a region near a section of the electrical power system that ismonitored by a GMD 102 that detected the intermittent fault. The serversystem 106 can use the weather data in combination with the intermittentfault data from the GMD 102 to identify a potential cause of theintermittent fault. For example, the server system 106 can correlate theweather data with the characteristics of the intermittent fault toidentify a potential cause of the fault. For example, if the weatherdata indicates strong winds in the region, the server system can send analert to utility personnel indicating that there is likely anenvironmentally caused fault (e.g., a tree branch) creating anintermittent ground connection in the monitored section of the powersystem. However, if the weather data does not indicate strong winds theserver system 106 may identify a different cause of the intermittentfault.

FIG. 4 is a flow diagram that illustrate a process 400 for detectingelectrical faults in electrical power systems. The process 400 can beperformed by one or more computing devices. For example, as discussedabove, the process 400 may be performed by the GMD 102 of FIG. 1.

The GMD measures a net electric field produced by two or more conductorsof an electric power system (402). For example, the GMD can obtainmeasurements from an electric field sensor of the net electric fieldpresent proximate to the sensor. For example, the GMD can obtain outputsignals from an electric field sensor that indicate the magnitude of thenet electric field proximate to the sensor. For example, the netelectric field proximate to the electric field sensor is the netelectric field that is measurable by the sensor. Put differently, thenet electric field proximate to the sensor is the electric field presentnear the sensor that creates measurable changes in the electric fieldsensor. In some implementations, the GMD queries the electric fieldsensor for measurements at a time interval. For example, the GMD can beconfigured to query the electric field sensor for measurements at aperiodic or an aperiodic time interval. In some implementations, the GMDcan vary the time interval in response to different criteria. Forexample, the GMD can increase the frequency at which it queries theelectric field sensor in response to detecting an electrical fault.

The GMD detects a change in the net electric field (404). For example,the GMD can compare successive measurements from the electric fieldsensor to detect changes in the measured net electric field. The GMD candetect a ground fault based on detected changes in the measured electricfield (406). For example, the GMD can determine based on the change inthe electric field that an electrical fault has likely occurred in oneof the two or more conductors. The GMD can determine that an electricalfault has occurred by comparing a subsequent electric field measurementto a previous measurement. For example, the subsequent electric fieldmeasurement may indicate an electrical fault if the magnitude of thesubsequent measurement is greater than that of the previous measurement.For example, if the magnitude of the electric field measurementincreases by a predetermined threshold value, the GMD can determine thata fault has likely occurred. In some implementations, the GMD canconfirm the existence of a fault by comparing the subsequent electricfield measurement with one or more fault severity threshold values. Insome implementations, the GMD can determine the severity of thepotential fault by comparing the subsequent electric field measurementwith one or more fault severity threshold values. For example, moresevere faults may be indicated by higher magnitude net electric fieldmeasurements.

The GMD sends data indicating the detection of the electrical fault to aserver system (408). For example, the server system can be a centralserver system configured to monitor for electrical faults from a networkof GMDs. The GMD can send the fault detection data to the server systemto enable the server system to provide appropriate alerts regarding theelectrical fault to computing devices associated with utility personnelwho are responsible for maintaining the operations of the electric powersystem. The fault detection data can include, but is not limited to, anindication that a fault has been detected, location informationassociated with the GMD, characteristics of the fault detection, or acombination thereof. Characteristics of the fault detection can include,but are not limited to, electric field measurement data indicative ofthe fault, times at which the measurements were taken, a severity levelof the fault, times at which the fault clears (e.g., for an intermittentfault), or a combination thereof.

In some implementations, the GMD can identify the electrical fault as anintermittent fault. For example, the GMD can compare a series ofelectric field measurements obtained over a period of time. The GMD candetermine that individual measurements in the series of measurementsindicate repeated increases and decreases in the net electric fieldmeasured by the electric field sensor that are indicative of repeatedfault detections and subsequent clearing of the faults. For example, themeasurements may repeatedly exceed and then fall below a fault detectionthreshold value.

In some implementations, the GMD can be configured to calibrate itsfault detection thresholds to account for the environment at thelocation in which it is installed. For example, the GMD can obtain aseries of electric field sensor measurements over a period of time(e.g., a calibration period), where each measurement in the series ofmeasurements indicates a value of the net electric field proximate tothe sensor at a respective time during the period of time. The GMD candetermine a baseline net electric field value for the location based onthe series of measurements. For example, the GMD can average themeasurements in the series. The GMD can calibrate the fault detectionthresholds by adjusting one or more of threshold values based on thebaseline net electric field value, or based on a factor thereof.

Although the operations of a GMD have been generally described inreference to detecting electrical faults in a three-phase AC electricalpower system, the GMD 102 can be configured for use with otherungrounded electrical power systems as well. For example, GMDs can beconfigured for use with ungrounded DC systems and other ungrounded ACsystems, e.g., ungrounded single phase or two-phase AC power systems.

FIG. 5 is a schematic diagram of a computer system 500. For example, thesystem, or portions thereof, can be implemented as the GMD controller orthe server system described above in reference to FIGS. 1 and 2A. Thesystem 500 can be used to carry out the operations described inassociation with any of the computer-implemented methods describedpreviously, according to some implementations. In some implementations,computing systems and devices and the functional operations described inthis specification can be implemented in digital electronic circuitry,in tangibly-embodied computer software or firmware, in computerhardware, including the structures disclosed in this specification(e.g., system 500) and their structural equivalents, or in combinationsof one or more of them. The system 500 is intended to include variousforms of digital computers, such as laptops, desktops, workstations,personal digital assistants, servers, blade servers, mainframes, andother appropriate computers, including vehicles installed on base unitsor pod units of modular vehicles. The system 500 can also include mobiledevices, such as personal digital assistants, cellular telephones,smartphones, and other similar computing devices. Additionally, thesystem can include portable storage media, such as, Universal Serial Bus(USB) flash drives. For example, the USB flash drives may storeoperating systems and other applications. The USB flash drives caninclude input/output components, such as a wireless transducer or USBconnector that may be inserted into a USB port of another computingdevice.

The system 500 includes a processor 510, a memory 520, a storage device530, and an input/output device 540. Each of the components 510, 520,530, and 540 are interconnected using a system bus 550. The processor510 is capable of processing instructions for execution within thesystem 500. The processor may be designed using any of a number ofarchitectures. For example, the processor 510 may be a CISC (ComplexInstruction Set Computers) processor, a RISC (Reduced Instruction SetComputer) processor, or a MISC (Minimal Instruction Set Computer)processor.

In one implementation, the processor 510 is a single-threaded processor.In another implementation, the processor 510 is a multi-threadedprocessor. The processor 510 is capable of processing instructionsstored in the memory 520 or on the storage device 530 to displaygraphical information for a user interface on the input/output device540.

The memory 520 stores information within the system 500. In oneimplementation, the memory 520 is a computer-readable medium. In oneimplementation, the memory 520 is a volatile memory unit. In anotherimplementation, the memory 520 is a non-volatile memory unit.

The storage device 530 is capable of providing mass storage for thesystem 500. In one implementation, the storage device 530 is acomputer-readable medium. In various different implementations, thestorage device 530 may be a floppy disk device, a hard disk device, anoptical disk device, or a tape device.

The input/output device 540 provides input/output operations for thesystem 500. In one implementation, the input/output device 540 includesa keyboard and/or pointing device. In another implementation, theinput/output device 540 includes a display unit for displaying graphicaluser interfaces.

The features described can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. The apparatus can be implemented in a computerprogram product tangibly embodied in an information carrier, e.g., in amachine-readable storage device for execution by a programmableprocessor; and method steps can be performed by a programmable processorexecuting a program of instructions to perform functions of thedescribed implementations by operating on input data and generatingoutput. The described features can be implemented advantageously in oneor more computer programs that are executable on a programmable systemincluding at least one programmable processor coupled to receive dataand instructions from, and to transmit data and instructions to, a datastorage system, at least one input device, and at least one outputdevice. A computer program is a set of instructions that can be used,directly or indirectly, in a computer to perform a certain activity orbring about a certain result. A computer program can be written in anyform of programming language, including compiled or interpretedlanguages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment.

Suitable processors for the execution of a program of instructionsinclude, by way of example, both general and special purposemicroprocessors, and the sole processor or one of multiple processors ofany kind of computer. Generally, a processor will receive instructionsand data from a read-only memory or a random access memory or both. Theessential elements of a computer are a processor for executinginstructions and one or more memories for storing instructions and data.Generally, a computer will also include, or be operatively coupled tocommunicate with, one or more mass storage devices for storing datafiles; such devices include magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,ASICs (application-specific integrated circuits).

To provide for interaction with a user, the features can be implementedon a computer having a display device such as a CRT (cathode ray tube)or LCD (liquid crystal display) monitor for displaying information tothe user and a keyboard and a pointing device such as a mouse or atrackball by which the user can provide input to the computer.Additionally, such activities can be implemented via touchscreenflat-panel displays and other appropriate mechanisms.

The features can be implemented in a computer system that includes aback-end component, such as a data server, or that includes a middlewarecomponent, such as an application server or an Internet server, or thatincludes a front-end component, such as a client computer having agraphical user interface or an Internet browser, or any combination ofthem. The components of the system can be connected by any form ormedium of digital data communication such as a communication network.Examples of communication networks include a local area network (“LAN”),a wide area network (“WAN”), peer-to-peer networks (having ad-hoc orstatic members), grid computing infrastructures, and the Internet.

The computer system can include clients and servers. A client and serverare generally remote from each other and typically interact through anetwork, such as the described one. The relationship of client andserver arises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinventions or of what may be claimed, but rather as descriptions offeatures specific to particular implementations of particularinventions. Certain features that are described in this specification inthe context of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

Thus, particular implementations of the subject matter have beendescribed. Other implementations are within the scope of the followingclaims. In some cases, the actions recited in the claims can beperformed in a different order and still achieve desirable results. Inaddition, the processes depicted in the accompanying figures do notnecessarily require the particular order shown, or sequential order, toachieve desirable results. In certain implementations, multitasking andparallel processing may be advantageous.

The invention claimed is:
 1. A ground fault detection device comprising:an electric field sensor; a power source; and a control system coupledto the electric field sensor and the power source, the control systemcomprising one or more processors and a data store coupled to the one ormore processors having instructions stored thereon which, when executedby the one or more processors, causes the one or more processors toperform operations comprising: obtaining output signals from theelectric field sensor at measurement intervals, the output signalsindicating respective values of a net electric field resulting from acombination of respective electric fields from two or more electricalpower transmission lines that are proximate to the electric fieldsensor; detecting, based on a change in at least one of the outputsignals, an electrical fault in at least one of the two or moreelectrical power transmission lines, wherein detecting the electricalfault comprises determining that a magnitude of the at least one of theoutput signals is greater than a magnitude of a previous output signal;and sending, at intervals to a server system, fault characteristic dataindicating one or more times at which measurements are taken thatindicate the electrical fault is detected and one or more times at whichmeasurements are taken that indicate the electrical fault has cleared.2. The device of claim 1, wherein the change in at least one of theoutput signals is a deviation from an approximately zero net electricfield measurement.
 3. The device of claim 1, wherein detecting theelectrical fault comprises determining that the magnitude of the atleast one of the output signals is greater than a threshold value. 4.The device of claim 1, wherein the electric field sensor is selectedfrom the group consisting of: a capacitor based electric field sensor,an electro-optical electric field sensor, a Micro-Electro-MechanicalSystems electric field sensor, or an antenna electrode sensor.
 5. Thedevice of claim 1, wherein the power source includes a battery or asolar cell.
 6. The device of claim 1, wherein the operations furthercomprise determining a severity of the electrical fault by comparing themagnitude of the at least one of the output signals with a plurality ofthreshold values, each threshold value in the plurality being associatedwith a respective fault severity level.
 7. The device of claim 1,wherein the fault characteristics include data indicating a magnitude ofthe electrical fault at times when the electrical fault is detected. 8.The device of claim 1, wherein the operations further comprisecalibrating the device by: obtaining a series of output signals from theelectric field sensor over a period of time, each output signal in theseries of output signals indicating a value of a net electric fieldproximate to the electric field sensor at a respective time during theperiod of time; determining, from the series of output signal, abaseline net electric field value; and adjusting one or more faultdetection thresholds based on the baseline net electric field value. 9.The device of claim 1, wherein the data indicating detection of theelectrical fault includes location data indicating a geographic locationof the device.
 10. The device of claim 1 further comprising a switchelectrically connected between the electric field sensor and an input tothe control system, wherein the electric field sensor comprises acapacitor, and wherein the operations further comprise: turning theswitch on, at a measurement interval, such that charge stored on thecapacitor is measured and the capacitor is discharged; turning theswitch off after the measurement interval; and entering a low powermode.
 11. The device of claim 1, wherein the operations further compriseidentifying the electrical fault as an intermittent fault.
 12. Thedevice of claim 11, wherein identifying the electrical fault as anintermittent fault comprises: comparing a series of output signalsmeasured over a period of time; and determining that individual outputsignals in the series of output signals indicate repeated increases anddecreases in the net electric field measured by the electric fieldsensor.
 13. A computer-implemented electrical fault detection methodcomprising: obtaining output signals from an electric field sensor atmeasurement intervals, the output signals indicating respective valuesof a net electric field resulting from a combination of respectiveelectric fields from two or more electrical power transmission linesthat are proximate to the electric field sensor; detecting, based on achange in at least one of the output signals, an electrical fault in atleast one of the two or more electrical power transmission lines,wherein detecting the electrical fault comprises determining that amagnitude of the at least one of the output signals is greater than amagnitude of a previous output signal; and sending, at intervals to aserver system, fault characteristic data indicating one or more times atwhich measurements are taken that indicate the electrical fault isdetected and one or more times at which measurements are taken thatindicate the electrical fault has cleared.
 14. The method of claim 13,wherein the change in the successive measurements of the net electricfield is a deviation from an approximately zero net electric fieldmeasurement.
 15. The method of claim 13, wherein detecting theelectrical fault comprises determining that at least one of thesuccessive measurements is greater than a threshold value.
 16. Themethod of claim 13 further comprising determining a severity of theelectrical fault by comparing at least one of the successivemeasurements with a plurality of threshold values, each threshold valuein the plurality being associated with a respective fault severitylevel.
 17. The method of claim 13 further comprising estimating alocation of the electrical fault within an electric system based on thefault characteristic data from the electric field sensor and secondfault characteristic data from a second electric field sensor.
 18. Themethod of claim 17, wherein estimating the location comprises comparingfirst timing data included in the fault characteristic data with secondtiming data included in the second fault characteristic data.
 19. Anon-transitory computer readable medium storing instructions that, whenexecuted by at least one processor, cause the at least one processor toperform operations comprising: obtaining output signals from an electricfield sensor at measurement intervals, the output signals indicatingrespective values of a net electric field resulting from a combinationof respective electric fields from two or more electrical powertransmission lines that are proximate to the electric field sensor;detecting, based on a change in at least one of the output signals, anelectrical fault in at least one of the two or more electrical powertransmission lines, wherein detecting the electrical fault comprisesdetermining that a magnitude of the at least one of the output signalsis greater than a magnitude of a previous output signal; and sending, atintervals to a server system, fault characteristic data indicating oneor more times at which measurements are taken that indicate theelectrical fault is detected and one or more times at which measurementsare taken that indicate the electrical fault has cleared.
 20. The mediumof claim 19, wherein the change in the successive measurements of thenet electric field is a deviation from an approximately zero netelectric field measurement.